Several attempts have been made to provide onboard indicators for the purpose of notifying an operator that the lubricating oil of an associated internal combustion engine is in need of being replaced.
For instance, U.S. Pat. Nos. 4,733,556 and 4,741,200 describe the use of sensors which directly measure various properties of lubricating oil and provide indications of when those properties change beyond predetermined limits.
Other systems have been described in which particular engine operating parameters are determined as being key to the effects of oil degradation and wear. Several patents, including the following, describe techniques for measuring operating parameters and inferring oil degradation based upon such measurements.
U.S. Pat. No. 4,506,337 teaches that soot suspended in lubricating oil is associated with its degradation and the amount of soot in the oil is strictly dependent on the number of engine revolutions, load, EGR rate. That patent presents a system for providing driver notification of the need to replace lubricating oil based upon a soot calculation algorithm in response to parameter inputs from an engine speed sensor and an engine load sensor.
U.S. Pat. No. 4,694,793 describes a system that senses the alkalinity and the oil level within the lubricating oil sump of an internal combustion engine. It is said that the reaction between alkaline content and metal contaminants in the oil increase with elevated temperature. Engine speed and temperature are used to predict the affect on the longevity of the oil from the standpoint of infusible matter contamination.
U.S. Pat. No. 4,525,782 describes a system that senses the lubricating oil condition indirectly by monitoring fuel consumption. In that patent a value corresponding to a specific quantity of fuel consumption is stored as a reference, and oil wear is determined as a function of the difference between the actual fuel consumed and the stored value.
U.S. Pat. No. 4,533,900 discloses a system that measures lubricating oil temperature, engine speed, and a rate of fuel consumption. It also measures distance traveled by the vehicle. In that system, a service warning is displayed after a predetermined distance has been traveled, wherein the distance is composed of the actual distance traveled and an additional engine loading component calculated as a function of the load on the engine.
U.S. Pat. No. 4,677,847 teaches a system that monitors the engine running time, the oil temperature and the engine speed to determine the rate of deterioration of lubricating oil. It provides a continuous output signal that represents the remaining useful life of the oil when desired by the driver. That system estimates a time in the future when the oil will reach undesirable deterioration levels. The time prediction is displayed as mileage remaining before the oil change is required.
U.S. Pat. No. 4,742,476 describes an automatic engine oil change indicator system in which only the engine oil temperature and engine speed are sensed to determine the wear life of lubricating oil in an internal combustion engine. An effective oil usage amount is periodically computed by multiplying accumulated engine revolutions (actual measured revolutions during the period) by a penalty factor which is determined as a sole function of the engine oil temperature as it relates to empirically determined data without regard to the engine load. Oil change indication is also provided by a one year clock or a 7,500 mile limit between changes.
U.S. Pat. No. 4,706,193 describes a system which senses the distance traveled by a vehicle, the temperature of the lubricating oil, the speed the engine is operating and the type of oil used. All sensor outputs are multiplied by weighted coefficients. They are added and that sum is integrated over time. When the integrated value exceeds a predetermined level, a warning signal is given to the driver. The described system also adjusts the predetermined level whenever oil is sensed as being added to that which is already present.
U.S. Pat. No. 4,497,200 discloses an engine oil evaluation indicator. The indicator includes an analog circuit which provides three currents that are summed and then integrated by an electrolytic integrating device. The three currents are proportionally provided to represent a temperature variation either below or above a satisfactory temperature, the idle periods of the engine and the utilization periods of the engine. When the integral of the sum reaches the maximum capacity of the device, a threshold detector senses the corresponding voltage increase across the device and warns the user that the oil must be replaced.